This investigation involves a study of the metabolic factors which govern the deformability of animal tumor cells. In addition, the effects of hormones and other chemical agents in regulating the flow of tumor cells both in vitro and in vivo will be examined. The premise of these experiments is that metabolic states or agents which affect either surface to volume ratios of tumor cells or the intrinsic fluidity of their plasma membrane components may have profound consequences on the ability of cells to transverse the microcirculation and to penetrate tissue spaces. The potential for the regulation of tumor cell deformability implicit in these experiments is highly relevant to the management of clinical problems of metastasis and invasiveness.